The present invention relates to a rotary seamer.
A seamer is a machine that enables to apply a lid to a container to close it hermetically, connecting the edge of the lid to the edge of the container by folding them onto each other.
Objects to be seamed generally have cylindrical geometry, e.g. they are constituted by pots or cans.
In practice, seaming is achieved by setting the container in rotation around its own axis, e.g. associating it to a mandrel and making it interact with a seaming tool, which in turn is rotating and appropriately shaped, i.e. shaped in such a way as to cause said folding of the container and of the corresponding lid.
In prior art solutions, the seaming tool is constituted by an idle roller.
Said roller is connected to an end of a lever integral with a rotating pivot. In this way, by rotating the pivot the roller is approached to or moved away from the object, moving the roller from an operative position, in which it interacts with the object seaming it, to a deactivated position, of non interference with the object.
The pivot, which consists of a rod-like element, is rotatably connected to a carousel, and it is rotated by interaction with a cam.
Moreover, in rotary seamers the treated objects are imparted a rotating motion around their own axis and a revolution motion around the axis of rotation of the carousel.
In this light, note that the velocity of rotation of the container around the axis of the carousel is linked to the speed of the production line, i.e. to the hourly rate of production of containers treated by the seamer. Instead, the rotation of the container around its own axis is linked to the finishing of the seaming process, said finishing increasing with the increase in the number of seaming turns, where the term “number of seaming turns” means the number of rotations the container completes relative to its own axis during the seaming of the lid.
The evolution of the materials of containers and lids requires ever more to advanced machinery to have better seaming results.
Moreover, the considerable differences within the range of the objects to be seamed, e.g. in terms of diameter or thickness or material used, imposes the need to adapt the seamer according to each case.
Therefore, seamers in use are provided with probes to measure the distance between the object to be seamed and the roller, and with systems to adjust said distance mechanically (and manually); the displacement of the roller is determined by the shape of the cam.
This entails two kinds of problems.
In the first place, said mechanical adjustments are complicated and costly and they are difficult to perform with precision (because they have to be carried out manually).
Secondly, the profile of the cam has to be redesigned in relation to the situation whereto corresponds the maximum rotation of the pivot; consequently, the profile of the cam is not optimized in all other situations.
Another problem is to vary the number of seaming turns. To increase the versatility of the seamer in handling containers and lids made of materials with different mechanical characteristics, it is necessary to be able to vary the number of seaming turns rapidly.
In this regard, while in known seamers the variation of the number of seaming turns is possible, it entails interventions that are costly in terms of time and of materials. In prior art solutions, changing the number of seaming turns requires replacing a series of gears or pulleys (situated with the body of the machine or possibly outside it) whose function is to transfer motion from a motorization to the mandrel that sets in rotation the object to be seamed.
This solution, in addition to being disadvantageous in terms of times and costs, presents the drawback of requiring to vary the velocity of rotation of the object. This solution does not allow to increase the number of seaming turns, for equal velocity of the object, by increasing the time during which the roller interacts with the object.
Additional technical problems are associated with the rollers.
A first problem derives from the need to house lubricated bearings within the roller, to allow it to rotate easily and freely; this is disadvantageous because it compromises the hygiene of the machines and the stiffness of the roller itself.
Another problem is determined by the fact that the impact between the roller and the object to be seamed (in the moment when they come in contact) entails a deterioration of the surfaces that come in contact, with inevitable failures due to the jamming of the machine caused by the material removed in said impact.